The present invention relates to the transmission and reception of millimeter, or micro waves, and more particularly, to a switched or time division duplex front end providing simplified circuitry which maintains isolation between signals of the receive and transmit signal paths.
Wireless communication, including both data communication and voice communication, provides a significant amount of communication bandwidth. However, wireless communication systems often include circuitry which is very complex and costly. Moreover, often equipment must be disposed in environments where it is subject to being damaged or destroyed. For example, front end equipment may be deployed up-mast, at or near an antenna system utilized by the communication system and, thus, may be subject to loss due to lightning strikes or wind or rain damage. Additionally, as space up-mast is limited, both due to physical constraints and aesthetic considerations, such equipment must be provided in as small a package as possible, often further driving up its cost.
Another design constraint on wireless communication systems is the limited amount of available spectrum for use by the plethora of users desiring to utilize such technology. Often, in order to provide multiple users with simultaneous communication capacity, the available spectrum is divided to be allocated among such users. Often this dividing of spectrum relies upon frequency division to assign a portion of the spectrum to each such user. However, such a division of the spectrum often requires a plurality of filters and associated circuitry in order to isolate each user""s signal from those of other users. This can both add to the cost of such a system as well as further compound the limited space problem described above.
Another way such spectrum may be divided for use amongst such users is to utilize time divisions of a communication signal in order to allot each user a portion of the communication carrier. However, such a time division system generally either requires frequency division in the forward and reverse links, introducing problems as described above, or adaptation to include duplex switching. Such duplex switching is generally difficult to implement as the circuitry itself is typically substantial, requiring substantial filters and circulators in order to isolate forward and reverse link signals and feedback problems associated therewith, also adding to the cost and further compounding the limited space problem.
A further disadvantage of such a time division system is often its inability to make efficient use of the available bandwidth. For example, where frequency division is relied upon to divide the forward and reverse links, one half of the available spectrum capacity may not be utilized at any one time as either the forward or reverse links will often remain idle, i.e., transmit no information, during communication in the other direction. A duplex switched system may make more efficient use of this available spectrum bandwidth, however such systems have here-to-fore been difficult to implement in broadband systems such as millimeter wave or microwave systems.
Therefore, a need exists in the art for a system and method for providing efficient use of available spectrum while providing equipment adapted to be disposed in harsh environments and environments presenting space constraints as well as to present a cost effective solution.
These and other objects, features and technical advantages are achieved by a system and method which provide a millimeter wave front end circuit which is adapted to utilize a reduced number and size of components preferably disposed in a rigid structure suitable for withstanding the environments into which it is placed. Accordingly, the front end structure of the present invention not only provides a cost effective solution, but also presents a reduced in size package agreeable with many installation scenarios.
A preferred embodiment of the present invention utilizes a rigid conductive plate structure in order to support and encapsulate the circuitry of the front end. Accordingly, the plates are formed to include cavities into which such circuitry may be disposed. By forming these cavities to be channels of predetermined dimensions waveguides may be formed to provide particular aspects of the desired circuitry without the addition of any actual components other than the plate structure itself. Preferably, the use of such waveguides according to the present invention includes waveguides tuned to be bandpass filters adapted to pass communicated frequency bands and reject out of band signals.
Moreover, to aid in isolation of forward and reverse links, as well as to provide signals having desired quality characteristics, the use of such waveguides includes waveguides tuned to be bandpass filters adapted to reject particular communicated signals. Accordingly, by disposing components of the front end circuit and/or signal paths associated therewith within these cavities, the circuits may be isolated from stray propagation of the communicated signals. The preferred embodiment of the present invention utilizes sufficiently small electronic circuitry, such as surface mount technology, in order that all, or substantially all, of this circuitry may be disposed completely within the confines of the rigid plate structure.
A preferred embodiment of the present invention utilizes the conductive nature of the plate structure in order to create microstrip transmission lines for the communication of signals. Accordingly, circuit cards composed of a dielectric material may be affixed to the plate structure such that the traces thereon in combination with the dielectric material and the underlying plate structure form a microstrip transmission line. The advantages of the microstrip transmission line are that false propagation passages may be eliminated or minimized and thus signal quality may be improved. Such an embodiment presents not only a mechanically sound structure, but also provides an inexpensive to manufacture design.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.